Geochemical characteristics of Jurassic high-sodium coal in Tatuo Coal Mine, Qinghai Province, China

Sodium in the coals of West China has received persistent attention due to its high contents and severe pollutions’ problems during coal utilization. A total of seven drill samples of the Jurassic coals from Tatuo coalfield, Qinghai Province, were collected and analysed using optical microscopy, scanning electron microscopy in conjunction with energy-dispersive X-ray spectrometry, X-ray powder diffraction, inductively coupled plasma mass spectrometry and X-ray fluorescence spectrometry. The results indicate that the Tatuo coal is of lower-high ash, medium volatile matter and ultra-low sulphur bituminous coal. Tatuo coal contains much more Na2O (> 2%), and belongs to high-sodium coal. The maceral index and element ratios of Sr/Cu, Fe/Mn and Sr/Ba showed that Tatuo coal was formed in a terrestrial peat swamp environment. The minerals in Tatuo coal, including clay minerals and halite, quartz, gypsum and rutile, are mainly concentrated in the bottom and top parts of the coal seam. Combined with scanning electron microscopy in conjunction with energy-dispersive X-ray spectrometry and optical microscope characteristics, the sodium could be carried into the peat/coal after the peat formation by basin fluids. The East Kunlun orogenic belt may be the main source of these minerals.